Stem cells may help heart pump more blood after attack

It looks as though a broken heart can mend itself, given a little technological assistance. Stem cells taken from the very organ that needs fixing may help it work better after a heart attack.

Cardiac stem cells can renew themselves and can form one of three types of cell that make up heart tissue. Roberto Bolli and his colleagues at the University of Louisville, Kentucky, reckoned that they might improve heart function if injected after a heart attack.

To find out, the team took stem cells from 16 people who had recently suffered a heart attack, multiplied them in culture and injected them back into each original patient's heart. In each case, the attack had reduced the patient's ejection fraction – the percentage of blood in the heart's ventricles that the heart pumps out in one beat – to less than 40 per cent. Ejection fractions should normally be between 50 and 65 per cent.

A new bypass

When a heart attack stops blood getting to heart tissue, some of the tissue dies. This can result in heart failure, in which its ability to pump blood is permanently decreased.

One routine treatment is coronary-artery bypass graft surgery, which diverts blood around a clogged vessel. During this surgery, Bolli's group took a small flap of tissue from each patient's heart. The researchers cultured around 1 million cardiac stem cells from each flap and injected into major blood vessels that lead to the heart once the patient in question had recovered from the operation.

The cell infusions were directly followed by a small balloon catheter, which was inflated four times for 3 minutes at a time to block the blood flow and help the cells to settle.

Take heart

Over the following year, Bolli's team monitored the patients' recovery, along with that of seven others who had had the same coronary-artery bypass graft surgery but not the stem-cell treatment. The team used echocardiography to measure heart volume and the amount of blood being pumped, and MRI to track the area of dead tissue.

Those who had received the stem-cell therapy saw their heart's ejection fraction increase from an average of 30 per cent to nearly 36 per cent a month later, and over 38 per cent four months down the line. In the eight people from this group that Bolli was able to check a year later, the average ejection fraction had increased to over 42 per cent. The size of the scar in these individuals was also smaller than in those who had not had the stem-cell therapy, and they reported a higher quality of life. The seven controls enjoyed no significant change in their hearts' ability to pump blood over the same period.

Safety first

As the study is a phase I clinical trial, its results can officially only be used to confirm the safety of the treatment. However, Michael Schneider at Imperial College London, who was not involved in the study, says that the work is "outstanding" in terms of "its rigour and scientific underpinnings".

It is unclear exactly how the treatment might have worked. "We don't know how much of the effect might be due to the formation of new beating heart cells, how much is due to activating dormant stem cells in the heart and how much is due to effects on wound healing, the formation of new blood vessels and inflammation," says Schneider.

Another possibility is that recovery was boosted by the inflation and deflation of the small balloon inserted into the blood vessels.

John Martin at University College London and Anthony Mathur at Barts and The London NHS Trust are conducting similar trials using stem cells derived from bone marrow. The pair point out that these types of stem cells, while not specific to the heart, are easier to get hold of and quicker to culture. Schneider thinks that cardiac stem cells are worth exploring further, however: "These cells, more than any others taken from the patient, have a well-proven ability to generate new heart muscle."

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